This invention relates generally to the field of control circuitry for appliances and more particularly to a circuit for powering-up a microprocessor based control.
Prior art microprocessor control circuits have generally required that the microprocessor be either in a power-on state at all times or be selectively powered up by the operator through an electromechanical switch. Generally, a system which is in a power-on state at all times is in a constantly stressed condition and is more susceptible to damaging line transients than a system which is electrically isolated from the power line.
Wong, U.S. Pat. No. 4,079,366 is an example of a circuit operable for maintaining the microprocessor in a power-on state at all times. In this type of a control a time of day clock is generally operated by the microprocessor control.
Marcade, in U.S. Pat. No. 4,195,232, discloses an on-off switch which projects through the control panel and is manually operable by the appliance user for providing power to the microprocessor control.
Prior art has shown microprocessor control circuits which are powered full time and circuits which are manually operated between an on and an off condition. Also shown has been the use of light emitting diodes and photo diodes to achieve electrical isolation of portions of the circuit. There has been no showing, however, of the use of an optocoupler in conjunction with a microprocessor control for achieveing selective energization of the microprocessor control through a touch-on membrane switch while maintaining electrical isolation between the touch-on membrane switch and the microprocessor control.